This invention generally relates to check valves, and more particularly relates to an apparatus for sealing leaking check valves.
Check valves are typically positioned in pipelines conveying gases and liquids such as oil, gas, air, and steam to prevent backflow. Backflow of the liquids or gases may result from pump trips or the like in which case the propelling force pushing the liquid or gas through the pipe is eliminated, resulting in such flow reversals. The typical construction of check valves includes a cylindrical valve body defining an axial passageway therethrough for fluid flow. The check valve also includes an integrally attached hollow tubular-like extension projecting generally perpendicularly from the pipe, the tubular extension having an open end. The open end of the tubular like extension is sealingly closed by a cap attached to the tubular extension by spaced-apart bolts positioned circumferentially around the cap. A gasket is interposed between the cap and tubular extension to prevent seepage externally of the check valve. A movable, hinged plunger is positioned within the valve body for controlling fluid flow through the passageway. The plunger includes a circular portion concentrically positioned within the valve body for preventing backflow through the valve body when the plunger is in the closed position. The plunger further includes a hinged arm rigidly attached at one end to the circular portion and hingedly or pivotally attached at its other end to the inner periphery surface of the tubular like extension. The hinged arm allows the circular portion to pivot or swing outwardly toward the tubular extension and out of the valve body passageway for allowing one-way flow through the pipe as is well known in the art. When backflow occurs, the circular portion returns to the central portion of the valve body to prevent backflow through the passageway.
Hazardous liquids and gases may flow through the pipeline and thus through the check valve. Therefore, due in part to environmental concerns, it has become increasingly important that the check valve be leak tight. It is desirable that liquids such as radioactive water flowing through pressurized water nuclear reactor pipelines not leak externally from the check valve in order to prevent any exposure of low level radiation to the environment. Pressurized water nuclear reactor pipelines are typically divided into two portions. One portion is the primary loop, which contains the radioactive water and a second portion is the secondary loop, isolated from the primary loop, which contains water that is essentially radiation free. It is equally desirable to have check valves on the secondary loop to mitigate any consequences of inadvertent pump trips, minimize pipe break accidents, and other system conditions such as slight leakages of water from the radioactive primary loop. In non-nuclear applications, valve leakage is a source of energy loss (i.e. steam leakage) and over time results in valve cap and body erosion.
The interface between the cap and the tubular extension created by bolting the cap to the tubular extension may create a flow path allowing liquids and gases to escape the check valve by flowing from the valve body passageway, into the tubular extension and along the interface between the cap and tubular extension. Thus, seepage is most likely to occur, if at all, through this interface. Seepage can occur due to factors such as poor assembly, gasket aging, or thermal pressure gradients.
A prior art solution for seepage from the check valve has been to seal the interface between the tubular extension and cap seal. There are two methods of implementing such a construction. One such method places a weld on the interface to seal the interface. Another method utilizes a double welded device. To utilize such a double welded device, an enclosing housing for the bolts and gasket interface of hollow toroidal configurations is welded to the tubular extension at two locations to enclose the interface. One of the latter locations being at the valve body side of the interface (i.e. to the tubular extension) and the other weld located at the toroidal housing interface with the cap and positioned inwardly of the bolts.
Recent regulations, such as Institute of Nuclear Power Operations' Significant Operating Experience Report 86-3, now recommends periodic inspection of the check valves to ensure integrity of valve (ie, that the valve is leak-tight). Such recommendations are in part a response to the concerns that the valve properly operate, particularly in nuclear reactor applications. To achieve this objective, frequent preventive maintenance inspections of the check valve are performed. The weldment formed during the one weld construction, as previously discussed, is difficult to grind out without damaging the seal between the cap and the tubular extension in performing such inspections and involves a time-consuming and tedious grinding process. Because the seal is welded it is difficult to grind out the weld without compromising the seal. The weldments formed during the double weld construction are also difficult to remove because two grinding processes are involved and damage may result to the cap or the tubular extension in the grinding process performed during such inspections. Such difficulty in removing the weldments of the double weld construction is in part due to an acute grinding angle.
Therefore, what is needed is an improved apparatus for sealingly enclosing the interface between the tubular extension and the cap to ensure that external seepage from the check valve is prevented, should the elastomeric seal become degraded or should it not be seated properly after routine maintenance activity.